The first group of migrants have been transferred from the humanitarian ship Aquarius - which had rescued 629 migrants crossing from Libya - to an Italian coast guard vessel, reports say.

Euronews correspondent Anelise Borges said the group consisted of 90 migrants, with more than 400 people remaining to be transferred according to an initial plan. Some 500 migrants are expected to be transferred to Italian navy and coast guard vessels.

The migrants will be taken by the Italian coast guard to Spain, but it is not yet clear if they will be taken there directly, or how the rest of the 629 will reach the Spanish mainland.

Home Affairs Minister Matteo Salvini told Italian media that a second humanitarian ship, the Sea Watch 3, which is currently navigating off the Libyan coast, will not be allowed into Italian ports, if and when it is involved in a migrant rescue operation.

The Italian government would adopt the same position with the Sea Watch 3 as it did with the Aquarius, Salvini said.

At around 4:30pm on Tuesday, the Sea Watch 3 said it was heading towards a shipwreck 20 miles from Libya in which 12 migrants were killed. A further 41 people, it said, had been rescued by a US Navy vessel.

"This happens, if there are not enough rescue assets in place and a safe passage is absent," the NGO said.

🔴 BREAKING #SeaWatch is heading towards a shipwreck 20 miles from Libya, reported to us by an order of the U.S. Navy, which has rescued 41 people from the water and confirms 12 corpses. This happens, if there are not enough rescue assets in place and a #safepassage is absent.